Cathode structure



Mgrch 16, 1943.

w. w. EITEL ET AL 2,314,037

CATHODE STRUCTURE I Filed June .30, 1942 2 Sheets-Sheet INVENTORS Q WILLIAM w. E TEL UAZ A. AE' Cl/ZLOUGH,

THEIR ATTORNEY CATHODE STRUCTURE a Filed June 30, 1942 Z Sheet'S-Speet 2 I INVENTORS WILL/AM w EI-TEL THEIR ATTORNEY Patented Mar. 16, 1943 was CATHODE STRUCTURE Villiam W. Eitel,

San Bruno,

and Jack A.

McCullough, Millbrae, Califl, assignors to Eitel- McCullough, Inc., San Bruno, Calif, a corporation of California Application June 30, 1942, Serial No. 449,149

9 Claims.

Our invention relates to a cathode structure for thermionic tubes.

It isamong the objects of our invention to provide an improved filamentary type cathode.

Another object is to provide a cathode having a structure and arrangement whereby breakage of filament wires during and after fabrication is largely eliminated.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of our invention. It is to be understood that we do not limit ourselves to this disclosure of species of our invention, as we may adopt variant embodiments thereof, within the scope of the claims.

Referring to the drawings:

Figure l is a perspective view of a tube embodying the cathode structure of our invention; and

Figure 2 is a fragmentary elevational View on approximately full scale showing the cathode and stem.

Figure 3 is a plan view on enlarged scale showing the top of the cathode; and

Figure 4 is a detail sectional view taken in a plane indicated by line 4-4 of Figure 2.

In terms of broad inclusion, our cathode structure comprises a pair of fixed supports; a movable support comprising a pair of overlying members; a plurality of hairpin filaments having their ends secured to the fixed supports and their bights secured between the members of the movable support; and means applying a force to the movable support for tensioning the filaments. The members of the movable support are secured together at points intermediate the interposed filaments so as to hold the latter by clamping pressure. The ends of the filaments are secured by welding, and clamping straps are provided on the fixed supports to hold the filament wires adjacent the welds.

In greater detail, and referring particularly to Figure l of the drawings, our improved cathode structure is embodied in an electronic tube comprising a suitable envelope 2. In the triode chosen for purposes of illustration plate 3 is supported on a lead 4 sealed to the top of the envelopes; and grid 6 is supported on a lead I sealed to a. side of the envelope. The lower end of the tube is fitted with a base 8 carrying the usual prongs 9. A reentrant stem II formed at the lower end of the tube provides a mounting for the cathode.

With particular reference to Figures 2 to 4, the cathode structure comprises a pair of leads I2 and a central standard I3, all preferably of tungsten and sealed in a press I4 on stem II. Flexible extensions I6 connect leads I2 with base prongs 9. A cup-shaped shield I1, preferably of nickel, secured to standard I3 protects the stem against heat and electron bombardment. On the upper end of each lead I2 is secured a fixed filament support I3; and on the upper end of standard I3 is disposed a movable filament support comprising a pair of overlying members I9.

Fixed supports it are arcuately-shaped brackets, say of tantalum, welded to leads I2 and arranged in circular formation about the central standard. Members IQ of the movable support are also preferably of tantalum; the lower member being a disk having an aperture slidably fitting the standard, and the upper member being a ring having an outside diameter approximately equalling that of the disk but having a larger center aperture, see Figure 3.

The cathode proper comprises a plurality of say three hairpin filaments, preferably of thoriated tungsten, secured at the lower ends to fixed supports I8 and held at the bights by the movable support. As shown in Figure 2, the filament ends overlap the fixed supports and are welded at the extreme lower ends only to the supports. Above the welds the filament wires 20 are clampingly held by straps 2!, also of tantalum, overlying the wires along the rim of the support and spot welded to the latter only at points adjacent the sides of, or intermediate the filaments. The filaments are thus welded at the lower ends and are clamped above the welds by straps 2|. This is for a special purpose.

In fabricating cathode structures of various kinds it is found that lateral or twisting stresses at the welds, due to handling the filaments, causes the welds to tear loose or the fine wires to break off close to the welds. Considerable loss is traceable to this fault. Our improved structure largely overcomes this problem because the wires are held by straps 2 I and the welds are relieved of lateral stresses. Since the filaments are held by clamping engagement only at the straps, and since the wires have not been weakened by heating at these points, there is little danger of their breaking off.

Another feature of our construction is that the bights of the filaments are also held by clamping engagement only between members I9, there being no weakening of the wires by heat, or welds to break loose, at the upper support. The wires lie between the disk and ring in cross-over relationship, and the two fiat members are spot welded together at points between the wires. This overcomes another serious breakage problem in filament fabrication.

The filaments are held under tension to maintain their spacing and alignment in the tube by means of a coil spring 22 encircling standard [3 and interposed between a stop 23 and a compression sleeve 24 extending upwardly and bearing against a cup-shaped piece 26 under the movable support. Caps 2'! at the ends of the stressed spring hold it centered. This arrangement places the spring well below the electrodes and away from the intense heat that would otherwise deteriorate the spring.

We claim:

1. A cathode structure comprising a support, a filament overlapping the support and welded thereto, and a strap clamping the filament to the support adjacent the weld.

2. A cathode structure comprising a support, a filament overlapping the support and welded thereto, and a strap overlying the filament adjacent the weld, said strap being welded to the support at opposite sides of the filament.

3. A cathode structure comprising a support, a plurality of filaments overlapping the support and welded thereto, and a strap overlying the filaments adjacent the welds and secured to the support at points intermediate the filaments.

4. A cathode structure comprising a pair of overlying supporting members, and a filament having a portion interposed between the members, said members being welded together at points on opposite sides of the filament to hold the latter by clamping pressure, said filament being spaced from the points of weld.

5. A cathode structure comprising a pair of overlying supporting members, and a plurality of hairpin filaments having their bights interposed between the members, said members being secured together at points intermediate the interposed filaments.

6. A cathode structure comprising a fixed support, a movable support comprising a pair of overlying members, a filament secured to the fixed support and having portions secured between said members of the movable support, and means including a compression member bearing against the movable support to tension the filament.

7. A cathode structure comprising a pair of fixed supports, a movable support comprising a pair of overlying members, a hairpin filament having its ends secured to the fixed support and its bight secured between the members of said movable support, the movable support lying in a plane disposed transversely to the plane defined by said filament, and means applying a force to the movable support to tension the filament.

8. A cathode structure comprising a pair of fixed supports, a movable support comprising a pair of overlying members, a plurality of hairpin filaments having their ends secured to the fixed supports and their bights interposed between the members of the movable support, said members being secured together at points intermediate the interposed filaments, and means applying a force to the movable support to tension the filaments.

9. A cathode structure comprising a pair of fixed supports, a movable support comprising a pair of overlying members a plurality of hairpin filaments having their ends overlapping and welded to the fixed supports, straps overlying the filaments adjacent the welds and secured to the fixed supports at points intermediate the filaments, the bights of the filaments being interposed between the members of the movable support, said members being secured together at points intermediate the interposed filaments, and means applying a force to the movable support to tension the filaments.

WILLIAM W. EITEL. JACK A. MCCULLOUGH. 

